Lens molds with protective coatings for production of contact lenses and other ophthalmic products

ABSTRACT

This invention relates to the preparation of molds for the production of contact lenses and other ophthalmic articles. By using an inorganic material to coat the optical surfaces and sidewalls of mold parts made from clear-resin materials, manufacturers can produce lens molds with greater dimensional stability and chemical resistance. In addition to protecting the clear resin from interaction with otherwise reactive monomers from which the molded article is made, such coatings can also be used to achieve preferential release of the molded article. The resulting mold is especially useful for providing an economical way to improve manufacturing quality of contact lenses.

This application claims the benefit of U.S. Provisional Application No.60/138,723 filed on Jun. 11, 1999.

TECHNICAL FIELD

This invention is directed to improved lens molds for the production ofcontact lenses, intraocular lenses, and other ophthalmic products. Inparticular, the invention involves protective coatings for allowing forthe use of mold materials having improved dimensional stability and/orincreased light transparency. The invention is also directed to a methodof making the improved lens molds and their use in the manufacture ofcontact lenses.

BACKGROUND

The molds used in the manufacture of soft (hydrogel) contact lenses havebeen made from a variety of rigid thermoplastic resins. For example,U.S. Pat. No. 5,540,410 to Lust et al and U.S. Pat. No. 5,674,557 toWidman et al. disclose mold halves made from polystyrene, polyvinylchloride, polyethylene, polypropylene, copolymers of polystyrene withacrylonitrile and/or butadiene, acrylates such as polymethylmethacrylate, polyacrylontrile, polycarbonate, polyamides such asnylons, polyesters, polyolefins such as polyethylene, polypropylene andcopolymers thereof, polyacetal resins, polyacrylethers, polyarylethersulfones, and various fluorinated materials such as fluorinated ethylenepropylene copolymers and ethylene fluoroethylene copolymers. Polystyreneis preferred by Widman et al because it does not crystallize and has lowshrinkage. An earlier patent, U.S. Pat. No. 4,661,573 to Ratkowski etal, discloses, for the processing of fluorosilicone copolymers intoextended wear lenses, molds formed of polypropylene, polyethylene,nylon, Teflon®, glass, or aluminum having its mold surfaces coated withTeflon® polymer.

The manufacturers of soft contact lenses have discovered that if themolds used to make the lenses are sufficiently inexpensive, it is moreeconomical to discard the molds after production of the lenses from themolds than it is to clean the molds to be reused. Polypropylene is agood example of an inexpensive resin that has been used to make moldsthat can be discarded at minimal cost. Another advantage ofpolypropylene is that unlike many resins, polypropylene can resistinteraction with the monomers used to make the contact lenses. Theability to resist chemical interaction prevents the lens and the moldfrom adhering to each other and simplifies their separation followinglens production.

Despite these benefits, however, polypropylene lens molds also sufferfrom several known disadvantages. One disadvantage is polypropylene'srelatively low dimensional stability. As mentioned by Widman et al,polypropylene partly crystallizes during cooling from the melt and is,therefore, subject to shrinkage, causing difficulties in controllingdimensional changes after injection molding. To improve dimensionalstability, manufacturers can make polypropylene lens molds thicker.However, while thicker polypropylene molds can have greater stability,they also require additional cooling time. The additional time needed tocool the thicker molds decreases the number of molds that can be madeper machine per unit of time. Furthermore, thicker and therefore largerpolypropylene molds can limit the number of molds per machine, therebyreducing product throughput. Finally, polypropylene's relatively poordimensional stability limits manufacturing yield, because the molds mayneed to be stored before use, for periods of up to several weeks in somecases, and many polypropylene molds fail to maintain dimensionalstability over time to a degree that eventually renders them unfit forlens production.

In addition to having relatively poor dimensional stability,polypropylene has other disadvantages. Polypropylene is a translucentresin that reduces the transmission of light. Typically, polypropyleneallows only about ten percent of light to pass through it. Poor lighttransmission reduces the speed of polymerization. Furthermore, theabsorption of oxygen by the molds, commonly experienced withpolypropylene molds, can influence lens quality. When the absorbedoxygen diffuses out, during lens molding, polymerization can beaffected, and lens surface quality can suffer as a result.

Several alternative resins offer greater dimensional stability and lighttransmittance than polypropylene. For instance, polycarbonate andpolystyrene are more amorphous resins and, therefore, have greaterdimensional stability than polypropylene. Moreover, these and other“clear” resins generally transmit at least 50% and often more than 70%of light.

Although polycarbonate and polystyrene resins offer greater dimensionalstability and light transmittance, they are vulnerable to chemicalinteraction with the monomers used in many soft contact lenses (forexample, N-vinylpyrrolidone and N,N-dimethylacrylamide, used in manyconventional contact lenses). Chemical interaction between the lensmonomers and the lens molds can cause the lens and the mold to adhere toeach other and, in a worst case scenario, the lens and the mold canbecome permanently joined. Moreover, in addition to being susceptible tochemical interaction, many clear resins are more expensive thanpolypropylene and are, therefore, too costly to discard.

Molds for making soft contact lenses have been treated to affect theirsurface properties. For example, U.S. Pat. No. 4,159,292 discloses theuse of silicone wax, steric acid, and mineral oil as additives forplastic mold compositions to improve the release of the contact lensfrom the plastic molds. U.S. Pat. No. 5,690,865 discloses an internalmold release agent such as waxes, soaps, and oils, including apolyethylene wax having a molecular weight of 5,000 to 200,000 or asilicone polymer having a molecular weight of 2,000 to 100,000. U.S.Pat. No. 5,639,510 to Kindt-Larsen discloses a surface-appliedsurfactant in the form of a uniform layer or very thin film or coatingto assist in the release from each other of mold components of amulti-part mold employed in the molding of hydrophilic contact lenses.Polymeric surfactants that can be used include polyoxyethylene sorbitanmono-oleates which are applied to a non-optical surface of the mold, butdo not cover the optical surface of the mold.

U.S. Pat. No. 5,674,557 to Widman et al discloses hydrophiliccontact-lens molds that are transiently modified with a removablesurfactant to provide a low water dynamic contact angle. This was foundto reduce lens hole defects in lens manufacture. Widman et al disclosesvarious polysorbates, ethoxylated amines, or quaternary ammoniumcompounds that can be applied to the mold surface by swathing, spraying,or dipping.

Mueller et al, in European Patent Application EP 0 362 137 A1, disclosesthe coating of molds with a co-reactive hydrophilic polymer likepolyvinylalcohol, ethoxylated PVA, or hydroxyethyl cellulose, in orderto provide a permanent hydrophilic coating on the lens. The mold coatingcopolymerizes with the lens material in the mold. Similarly, Merill, inU.S. Pat. No. 3,916,033, discloses coating the surface of a mold withpolyvinylpyrrolidone to form a coating that is later to come intocontact with a previously crosslinked silicone lens. Merill teachesspreading a coating solution over the mold while held in a chuck,thereby achieving a fairly uniform coating of several thousandths of aninch, after which the wet film is allowed to dry to form a hard glassypolymer layer of about 1 to 5 thousandths of an inch. Finally, monomericN-vinyl pyrrolidone is dissolved in the coating ready for contact withthe silicone lens. As one other example, U.S. Pat. No. 5,779,943 to Ennset al. discloses coating a mold with a hydrophobic latent-hydrophilicmaterial, after which a lens material is molded therein. During curing,the mold coating is apparently transferred to the lens surface. The lensis then treated to convert the coating to a hydrophilic form.

It is an object of our system to provide the manufacturer of contactlens and other ophthalmic articles placed on or in the eye with animproved way to mold them, by providing molds with greater lighttransparency or dimensional stability which can be stored for anextended period of time while, concurrently, maintaining the chemicalresistance of the molds to a variety of monomers used in making theophthalmic articles. This combination of mold properties can beeconomically achieved by use of the present invention, and may even beachieved in molds that are discarded after a single use.

SUMMARY OF THE INVENTION

Our system uses clear-resin lens molds with protective coatings for theproduction of contact lenses, intraocular lenses, delivery devices, andother such ophthalmic articles. Clear resins are not only more amorphousand, therefore, more dimensionally stable than polypropylene, but arealso capable of transmitting a greater percentage of actinic light.Various clear resins are suitable for contact lens molding purposes,including polyvinyl chloride (PVC), polyester, polysulfone,polyacrylate/polymethacrylate, polycarbonate, and polystyrene.

Polycarbonate, polystyrene, or polyacrylate materials are particularlypreferred. These resins offer great dimensional stability and lighttransmittance; but unlike many other clear resins, they are alsorelatively inexpensive. Despite the advantages associated withclear-resin lens molds, it is commonly known that clear resins have atendency to interact with monomers used in contact lens production.Until now, manufacturers have only been able to develop a limited numberof clear-resin lens molds that can effectively resist chemical monomerinteraction. Unfortunately, existing clear-resin lens molds may be tooexpensive, especially to discard after single-use, or may only offerresistance to limited kinds of monomer materials used in the manufactureof ophthalmic articles.

The present invention is directed to clear-resin molds and methods ofproducing clear-resin molds, used for making ophthalmic articles, havinga permanent (non-transient), dense, uniform, and continuous protectiveinorganic coating on the surface of the mold, including at least theoptical surfaces thereof, to prevent adverse monomer chemicalinteractions. Although several coating techniques are capable ofapplying such a coating, including evaporation, sputtering, spraying,and photo-chemical vapor deposition, the preferred embodiment forapplying a protective coating to the mold employs plasma-enhancedchemical vapor deposition (PECVD) or other plasma glow dischargetechniques, which make such coatings generally uniform, continuous,dense, and pinhole free. The coating, during molding of the ophthalmicarticle, is essentially inert or non-reactive with the lens monomers orlens surface that is formed in the mold assembly. On the contrary, thepurpose of the coating is to prevent chemical interaction of the moldwith the polymerizable monomers used in making the opthalmic article.

A variety of inorganic coating materials that can be used to preventmonomer chemical interaction with the underlying mold surfaces. Suitablecoatings include silicon and metal oxides, carbides, and nitrides. Ofthese, SiO_(x), SiON, Si₃N₄, TiO₂, Ta₂O₅, and Al₂O₃ have been found tobe particularly effective. These inorganc coatings, which do not containcarbon as a principal element, can have minor amounts of carbon or H andmay be formed from carbon-containing compounds or precursors.

Although the above-listed coating materials are preferred because oftheir ability to transmit actinic radiation and to protect againstmonomer interaction, there are other materials that, despite theirdiminished capacity to transmit light, can be used to prevent monomerinteraction. Furthermore, materials for contact lenses, for instance,can also be cured by sources of energy other than light (for example, byheat or microwave energy wherein transmission of light is unnecessaryfor curing). In such cases, metal nitrides such as TiN or AlN or metalcarbides such as TiC or SiC, which do not transmit light, can be used toprotect against monomer interaction with the mold material. Moreover,even when employing light to cure a lens material, it may not beessential that light be able to transmit through both female and malemold parts since light is generally directed from only one side of thelens mold. Therefore, in cases where light for curing a lens or otherarticle only needs to be directed from one side, mold materials withlimited light transmittance can be applied only to the mold cavitysurfaces through which light transmission is not essential. For example,by coating one mold part with a light-transmitting coating material andthe other with a coating material having poor light transmittance,manufacturers can produce a clear-resin lens mold that is well suitedfor contact lens production.

Although a single coating can be used to protect the cavity surfaces ofmold parts, multiple coatings formed from different materials can alsobe used. Even if more costly to apply multiple coatings to the moldcavity surfaces, the presence of multiple layers may provide enhancedprotection against monomer interaction and may facilitate release of amolded article from the mold. For example, anywhere from one to fivelayers or more of an inorganic coating can be economically applied to amold part. Also, besides preventing monomer interaction with clearresins used to make mold parts, additional advantages of significancecan also be obtained by use of mold coatings according to the presentinvention. For example, mold coatings according to the present inventioncan also be used to improve mold separation, prevent adhesion, andachieve preferential release.

By eliminating the risk of chemical interaction, manufacturers can moldcontact lenses or other ophalmic products using clear-resin molds withimproved dimensional stability and light transmittance. Moreover, theapplication of a coating to the mold cavity surfaces can also accomplishpreferential release. For example, our system simplifies and economizeslens production by reducing mold cycle time, increasing productthroughput, improving lens quality, and increasing the speed ofpolymerization.

These and other objects of the invention can be better understood byreference to the Sole Figure in combination with the following detaileddescription of the invention.

DRAWING

FIG. 1 (Sole FIGURE) is a cross-sectional view of a monomer-filledcontact lens mold with an applied protective coating according to thepresent invention.

DETAILED DESCRIPTION

Although the invention is applicable to the molding of a variety ofophthalmic products placed on or in the eye, for example, intraocularlenses, contact lenses, delivery devices for therapeutic agents, and thelike. The invention is especially useful and advantageous for castmolding soft or hydrogel contact lenses. By way of example, therefore,the invention will be described with reference to the molding of acontact lens.

Referring to FIG. 1, a representative mold assembly 5 according to thepresent invention is shown. The mold assembly includes posterior mold 7having a posterior mold cavity defining surface 2 (which forms theposterior surface of the molded lens) and anterior mold 6 having ananterior mold cavity defining surface 3 (which forms the anteriorsurface of the molded lens). Each of the mold sections is injectionmolded from a clear resin in an injection molding apparatus. When themold sections are assembled, a mold cavity is formed between the twodefining surfaces that correspond to the desired shape of a contact lens8 molded therein. Because monomer overflow often occurs during clampingof the lens mold parts during production, the anterior lens mold part 6is often configured to include a monomer overflow reservoir 9.

In general, molded lenses are formed by depositing a curable liquid suchas a polymerizable monomer and/or macromer into a mold cavity, curingthe liquid into a solid state, opening the mold cavity and removing thelens. Other processing steps such as hydration of the lens can then beperformed. Conventional molding techniques and the details of moldstructures in a particularly preferred embodiment are disclosed, forexample, in commonly assigned U.S. Pat. No. 5,466,147 to Appleton etal., herein incorporated by reference in its entirety. Otherconventional molding techniques and molds that can be used in accordancewith the present invention (for example, wherein a plurality of malesections having convex molding sections and a plurality of femalesections having concave molding surfaces are integrally formed orcommonly supported on frames) are disclosed in U.S. Pat. No. 5,820,895to Widman et al, U.S. Pat. No. 5,540,410 to Lust et al, and U.S. Pat.No. 4,640,107 to Larsen.

In the embodiment of FIG. 1, the mold assembly 5 for molding soft(hydrogel) contact lenses uses clear-resin molds 5 with treated cavitysurfaces 2, 3 to prevent monomer chemical interaction. As mentionedabove, clear resins are more amorphous and more dimensionally stablethan crystalline resins. To ensure mold performance, we prefer to use aclear resin that has sufficient dimensional stability. In the finalmold, any deviations from the intended radius of curvature of the moldsare within ±20 microns up to six months after their production,preferably for any period from one day to six months after theirproduction, while the molds are at room temperature, namely about 25° C.In addition to having greater dimensional stability, clear resins canalso transmit a greater percentage of actinic light energy. Again, toensure optimum mold performance, we prefer to use a clear resin that cantransmit at least 20% of actinic light energy, preferably at least 50%of the actinic light emitted from the light source, in the case of alens manufacturing process employing UV curing. However, the presentinvention is not limited to manufacturing processes employing curing bylight energy, and the molds described herein can be designed, by way ofexample, for thermal or microwave curing, in which case lighttransmission is no longer important.

There are many clear resins that are suitable for molding soft lenses,including: polyvinyl chloride (PVC), polycarbonate, polystyrene,polyester, polysulfone, and polyacrylate/polymethacrylate. Of these, weprefer to use either polycarbonate, polystyrene, or polymethacrylate,which offer improved dimensional stability and light transmittance andwhich are also available to manufacturers at a relatively low cost. Thisreduces the expense associated with discarding the molds 5 after use,according to a preferred process of the present invention.

As mentioned above, although clear-resin lens molds 5 are, in many ways,well suited for contact-lens production, they are vulnerable to monomerchemical interaction. To prevent undesirable monomer interaction, wecoat the optical surfaces 2, 3 of the lens mold parts with a dense,uniform, and continuous protective coating 11. Moreover, we also preferto coat the cavity side-walls 12, 13 of each mold part to furtherfacilitate separation and to prevent adhesion. The coating 11 acts as abarrier between a lens monomer 8 and the lens mold cavity surfaces andprevents interaction. By preventing interaction, manufacturers can keepthe lens mold 5 and lens monomer 8 from adhering and becomingpermanently joined during production.

The protective mold coating is non-reactive with the lens material inthe mold. The protective coating should have sufficient thickness toprevent interaction of the mold material with the monomers used to makethe lens. An effective coating is typically between 10 nm and 5 μmthick. It is also desirable to apply the protective coating so that allmold cavity surfaces of the lens mold parts are adequately coveredincluding mold grooves and curved surfaces.

The coating 11 should be applied using a technique that guaranteescoating density, thickness, uniformity, and continuity. Various coatingtechniques are commercially available for applying protective coatings11 to mold surfaces including: evaporation, sputtering, dip/spincoating, spraying, photo-chemical vapor deposition, plasma-enhancedchemical vapor deposition (PECVD), and other plasma glow dischargetechniques. Of these, we have found it to be particularly advantageousto use PECVD applied coatings. PECVD involves creating plasma in thevapor phase using means such as RF excitation to activate or stimulate areaction between coating materials and reactants. Generally, a liquidprecursor material is vaporized and introduced along with an oxidizerinto a vacuum chamber. The liquid precursor is subsequently decomposedand reacted to form a film under plasma conditions. The vacuum requiredfor this process is moderate compared to other deposition technologies,and the coating growth rate is high. Moreover, the reaction can beachieved without having to introduce additional heat. PECVD coatings areideal for lens production purposes; the coatings are glass-like,flexible, thin, dense, uniform, continuous, and pin-hole free.

Although the technique used to apply the protective coating 11 issignificant, it is equally important to select an appropriate coatingmaterial. A suitable coating material must be resistant to lens monomerchemical interaction. When light is used to cure the lens, the coatingmaterial should be capable of allowing the transmission of light energy.Again, numerous coating materials are available that exhibit thesecharacteristics. Some suitable materials include silicon and metaloxides, nitrides, and carbides. Such inorganic materials can be formedfrom inorganic compounds and/or by certain organic or organometalliccompounds which are precursors to the coating material. For example,TMDSO (trimethyldisiloxane) can be used as a precursor of a siliconoxide inorganic coating that may contain minor amounts of carbon interms of relative mole percent and at least about 70% (mole percent) ofthe non-carbon containing component (silicon dioxide), more preferablyat least about 90% of the non-carbon containing component (silicondioxide).

Examples of effective coating materials that are preferred include:SiO_(x), SiON, Si₃N₄, TiO₂, Ta₂O₅, and Al₂O₃, especially for the moldingof contact lenses empolying UV curing. However, when lens manufacturersdo not need molds that transmit actinic light energy, they can also usecoating materials that do not transmit actinic light. Materials likemetal nitrides and metal carbides, for instance TiN, AlN, TiC, and SiC,are effective in preventing monomer interaction but are relatively poortransmitters of light energy. Since actinic radiation is often directedfrom only one side of the lens mold 5 during curing, lens makers canproduce a clear-resin lens mold assembly 5 that has one mold part thatis coated with a light-transmitting coating material and a second lensmold part coated with a coating material that has poor lighttransmittance. A lens mold assembly 5 coated in this manner is wellsuited for lens production.

The applied coating 11 can be a single-layer, single-material coating;or alternatively, the coating 11 can also include multiple layers ofdifferent coating materials. Although multi-layering will increaseproduction costs, it may improve the resistance to monomer interaction.

In addition to preventing undesirable monomer interaction, our coatedlens mold assembly 5 can also provide preferential lens release.Preferential release involves the ability of lens makers to make lensmolds that are capable of causing a finished lens to stay consistentlywith one of either the posterior or anterior mold part upon release. Inother words, it refers to the ability to make the lens mold so that thefinished lens remains with a “preferred” lens mold part upon separation.By selecting the appropriate coating materials for both the female andmale mold sections, lens makers can alter the hydrophobic or hydrophilicquality of the lens mold cavity coatings and can achieve preferentialrelease. For example, by controlling the ratio of oxygen to precursorused to form a mold coateing, for example in forming an silicon oxidecoating, the coating, the relative hydrophilicity of the coating can beadjusted. The higher the ratio, the more hydrophilic the coating. Thus,by selecting the appropriate coating materials, lens makers caneffectively adjust the hydrophilic or hydrophobic quality of the moldcavity coatings 11 and can establish a “preferred” mold part. In doingthis, lens makers can essentially alter the mold cavity surfaces so thata finished lens will remain with only the intended lens mold part,either the anterior or the posterior as the case may be, uponseparation. The ability to achieve preferential release is beneficialnot only for clear-resin molds, but can also be used in lens molds madefrom materials that are not vulnerable to monomer interaction.

The resulting mold assembly 5 exhibits improved dimensional stabilityand light transmittance and can optionally also achieve preferentialrelease. By using our mold assembly 5, contact lens manufacturers cansimplify and economize lens production by reducing the lens mold cycletime, improving lens quality, increasing polymerization speed, andincreasing production throughput. It should be noted that coated moldsas described herein can be used in the thermal curing of the same orsimilar formulations and monomers as used in light curing to give shapedarticles such as contact lenses. Alternatively, for example, a UV maincure can be followed by a thermal secondary cure (heat post-cure).

The following specific experiments and examples demonstrate thecompositions and methods of the present invention. However, it is to beunderstood that these examples are for illustrative purposes only and donot purport to be wholly definitive as to conditions and scope.

EXAMPLE 1

This Example illustrates the preparation of a contact lens mold with asilicon nitride coating using plasma-enhanced chemical vapor deposition(PECVD). Polystyrene molds were placed in a stainless steel chamberequipped with a capacitatively coupled radio frequency (13.56 MHz) powersupply. The chamber was evacuated using a turbo-molecular pump. Afterpumping down to a base pressure of 10⁻⁴ Torr, working gases wereadmitted using mass flow controllers (MFC). The desired pressure wasachieved using a throttle value and a MKS baraton capacitance pressuregauge. The process gases used for the silicon nitride deposition(wherein the ration of silicon to nitrogen was approximately 2.3)included silane and ammonia (SiH₄/NH₃) in a 1:4 ratio. The depositionpressure was 80 to 100 mTorr, and the substrate temperature duringdeposition was approximately 40 to 60° C. The flow rates of SiH₄ and NH₃were 10 to 20 and 40 to 80 sccm, respectively. The coating thickness wasin the range of 60 nm to 120 nm.

EXAMPLE 2

This Example illustrates the preparation of a contact-lens mold with asilicon oxide coating using plasma-enhanced chemical vapor deposition(PECVD). Using a setup similar to the setup described in Example 1, acontact lens mold was coated with silicon oxide. The working gases usedto obtain the coating was trimethyldisiloxane and oxygen wherein theratio of trimethyldisiloxane to oxygen was 1:2. The coating thicknesswas between 600 nm and 1000 nm.

EXAMPLE 3

This Example illustrates the chemical resistance of plastics coatedaccording to the present invention. Flat samples of amorphous plastics(polystyrene, polycarbonate, and polysulfone) were exposed to one dropof Monomer Mix A and B used for lens casting, respectively anon-silicone soft lens and a silicone soft lens. Monomer Mix A comprisedthe following components: 2-Hydroxyethyl methacrylate (32 parts),N-vinyl pyrrolidone or NVP (45 parts), 2-Hydroxy-4-t-butylcyclohexylmethacrylate (8 parts), ethyleneglycol dimethacrylate (0.1 parts),methacryloxyethyl vinyl carbonate (0.5 part), glycerine (15 parts), apolymerizable blue tint (150 ppm), and an initiator Darocur (0.2 parts).Monomer Mix B comprised the following components: apolyurethane-polysiloxane prepolymer derived from isophoronediisocyanate, diethylene glycol, αω-hydroxybutyl polydimethylsiloxane ofmolecular weight 4000, and 2-hydroxyethyl methacrylate at the molarratio of 6:3:2:2 (50 parts), 3-methacryloxypropyltris(trimethylsiloxy)silane or TRIS (20 parts), N,N-dimethyl acrylamideor DMA (30 parts), N-hexanol (20 parts), a benzotriazole-basedpolymerizable UV blocker (0.5 parts), a polymerizable blue tint (150ppm), and a photoinitiator, Igracure-819 (0.5 part). After five minutes,the monomer drops were rubbed away using a kimwipe. After removing themonomer, the samples were observed. The surfaces of the plastic sampleshad become rough and opaque, indicating that there had been aninteraction with the monomer ingredients (DMA or NVP). However, when thesame monomer mixes were applied to silicone nitride-coated polystyrenemolds according to Example 1, there was no change in surface appearance.

EXAMPLE 4

This Example illustrates lens casting (with the Monomer Mix A of Example3) by cast molding, using polystyrene molds with PECVD-applied siliconnitride coatings according to Example 1. Anterior mold parts werecharged with 60 mg (more than needed) of the monomer mix. The anteriormold parts were then capped with posterior mold parts. The molds wereclamped and placed under an UV light source for 15 minutes. Following UVirradiation, the molds were then heat cured in an oven at 60° C. for 60minutes to ensure that the monomer mix was fully cured. After curing,the molds were found impossible to separate. This was due to thereservoir area of the molds not being sufficiently coated with siliconnitride, resulting in chemical attack of the uncoated mold surface inthat reservoir area by the monomer mix in the reservoir area,particularly after capping the mold.

In a second attempt, an anterior mold was charged with 28 mg of monomermix such that the mold cavity (between posterior and anterior moldparts) was underfilled, meaning there was no monomer overflow thatentered the improperly coated mold reservoir. After repeating the curingprocess set forth above, the molds were easily separated. Followingseparation, the lens stayed with the anterior mold part and was laterreleased in water. These results indicated that the surface of thecoated mold provided good chemical resistance to the monomer mix.

EXAMPLE 5

This Example illustrates lens casting (of the Monomer MIX B in Example3) by cast molding using polystyrene molds with PECVD-applied siliconnitride coatings. The anterior mold parts were charged with 60 mg (inexcess of what is required) of monomer mix and then capped withposterior lens mold parts. The overflow of the monomer mix was collectedby the lens reservoir. In addition, some of the anterior mold parts werecharged with 28 mg of monomer mix such that the mold cavity (between theposterior and anterior mold parts) was under-filled. The molds were thenclamped and placed under a visible light source for 60 minutes to curethe monomer mix. All the molds that were underfilled were easilyseparated. (Some compositions, such as certain silicone hydrogels can beeasily separated irrespective of underfilling or not.) Followingseparation, the lenses which stayed with the posterior mold parts werereleased from the molds in less than one hour in a 50/50water/isopropanol solution. The surface characterization of the lensesindicated that there was no silicone nitride on the lens surface.

Many other modifications and variations of the present invention arepossible in light of the teachings herein. It is therefore understoodthat, within the scope of the claims, the present invention can bepracticed other than as herein specifically described.

We claim:
 1. A mold assembly for the manufacture of at least oneophthalmic article used in or on the eye, which mold assembly comprisesa mateable pair of mold parts made from a clear-resin mold materialwherein the cavity surfaces of the mold parts comprises a coating of aninorganic material to protect the mold parts from attack by monomer usedin making the ophthalmic article, which protective coating ispermanently and externally applied to the cavity surfaces of the moldassembly and is essentially non-reactive with the surface of theophthalmic article formed by the mold system.
 2. The mold assembly ofclaim 1, wherein the ophthalmic article is a contact lens or anintraocular lens.
 3. The mold assembly of claim 1 or 2, wherein the moldparts are injection molded and have sufficient dimensional stability sothat any departures from the intended radius of curvature are within+/−20 microns for all periods of time between one day and six monthsafter production of the mold parts.
 4. The mold assembly of claim 3,wherein the clear resin used to make the mold transmits more than 20% ofUV light, in the case of a lamp used to cure the lens material.
 5. Themold assembly of claim 1, wherein the protective coating comprises asilicon-containing material.
 6. The mold assembly of claim 1, whereinthe protective coating comprises one or more metal oxides.
 7. The moldassembly of claim 1, wherein the protective coating is uniform,continuous, and sufficiently dense to form a barrier to monomerdiffusion.
 8. The mold assembly of claim 1, wherein the coating has beenuniformly applied using plasma-enhanced chemical vapor deposition(PECVD).
 9. The mold assembly of claim 1, wherein the coating is between10 nm and 5 μm thick and is permanently affixed to the mold surface. 10.The mold assembly of claim 1, wherein the mold is made from a materialselected from the group consisting of polyvinyl chloride (PVC),polycarbonate, polystyrene, polyester, polysulfone, polyacrylate, orpolymethacrylate.
 11. The mold assembly of claim 1, wherein theprotective coating comprises silicon oxide, silicon nitride or amaterial consisting of silicon, oxygen, and nitrogen.
 12. The moldassembly of claim 1, wherein the protective coating comprises TiO₂ orTiN.
 13. The mold assembly of claim 1, wherein the protective coatingcomprises Ta₂O₅.
 14. The mold assembly of claim 1, wherein theprotective coating comprises Al₂O₃.
 15. The mold assembly of claim 1,wherein the protective coating comprises multiple layers of differentcoating materials.
 16. The mold assembly of claim 1, wherein each of themold parts is coated with a different coating material.
 17. The moldassembly of claim 1, wherein the inorganic coating contains minoramounts of carbon.
 18. A mold assembly for the manufacture of at leastone soft contact lens, which mold assembly comprises at least oneanterior and one posterior mold part molded from a clear resin thattransmits at least 20% of actinic light and has sufficient dimensionalstability to limit any deviations from intended radius of curvature to+/−20 microns within any period from one day to six months after moldproduction, wherein the mold parts each have a protective inorganiccoating that is 10 nm to 5 μm thick, which coating is non-reactive withthe lens formed by the mold assembly, and whereby the coating protectsthe cavity surfaces of the lens mold from chemical attack by themonomers used to form the lens in the mold.
 19. The mold assembly ofclaim 18, wherein the resin used to make the mold has greaterdimensional stability and higher light transmittance than polypropylene.20. The mold assembly of claim assembly 18, wherein the resin ispolycarbonate, polyacrylate, or polystyrene.
 21. The mold assembly ofclaim 18, wherein the posterior mold part has a reservoir to collectmonomer overflow produced during lens production and wherein the coatinghas been applied to protect the overflow reservoir as well as the moldcavities.
 22. The mold assembly of claim 18, wherein the coatinguniformly and continuously covers the lens molds and protects the moldfrom attack by polyvinylpyrrolidone or dimethylacrylamide monomer.
 23. Amethod of molding an ophthalmic article for use in or on the eye,comprising the following steps: a) injection molding the parts of aclear-resin mold assembly comprising at least one anterior and oneposterior mold part for production of the ophthalmic article; b)permanently affixing a uniform and continuous protective coating of aninorganic material to at least one of the cavity surfaces of the moldparts to protect the surfaces from chemical attack by the monomers usedto make the ophthalmic article being molded; and c) cast molding atleast one ophthalmic article using the mold assembly, wherein itsprotective coating does not react or coat the surface of the ophthalmicarticle.
 24. The method of claim 23, wherein the ophthalmic article isan intraocular lens or a contact lens.
 25. The method of claim 23,comprising the step of selecting a mold resin for a mold part that hassufficient dimensional stability to limit deviations from intendedradius of curvature of the mold part to +/−20 microns within a period ofone day to six months from the time of producing the mold part.
 26. Themethod of claim 23, comprising applying the protective coating to themold using a technique that produces a dense, uniform, and continuousprotective coating.
 27. The method of claim 23, including coating amonomer overflow reservoir along the posterior mold part's circumferencewith the protective coating to protect the reservoir from monomerchemical attack.
 28. The method of claim 23, including applying thecoating to the mold using plasma-enhanced chemical vapor deposition(PECVD).
 29. The method of claim 23, wherein the inorganic materialcomprises silicon.
 30. The method of claim 28 wherein precursor of thecoating comprises carbon even though the inorganic coating producedtherefrom contains no carbon or carbon in only minor amounts.
 31. Themethod of claim 23, including the step of coating mold cavity surfaceswith multiple layers of different coating materials.
 32. The method ofclaim 23, including applying a different coating material to the cavitysurface of each mold part.
 33. The method of claim 23, includingapplying a protective coating to both mold cavities and adjusting thehydrophilic or hydrophobic quality of each protective coating to inducepreferential release of the ophthalmic article that is made by the moldassembly.
 34. The method of claim 33, wherein the hydrophilic orhydrophobic quality of each protective coating is adjusted by the amountof oxygen, or weight ratio thereof to the precursor compound, used informing the inorganic coating.
 35. The method of claim 23, includingapplying a coating material capable of transmitting actinic light to thecavity surface of at least one lens mold part through which actiniclight energy is directed and applying a second coating material offeringsubstantial protection against monomer interaction but lackingsufficient light energy transmittance to the mold cavity surface of themold part through which curing energy is not directed.
 36. The method ofclaim 23, wherein the mold assembly is used once to make an ophthalmicarticle and then discarded.
 37. A method of molding at least one softcontact lens comprising the following steps: a) injection molding theparts of a clear-resin mold assembly comprising at least one anteriorand one posterior lens mold part for contact-lens production, whereinthe mold part has sufficient dimensional stability to limit deviationsfrom intended radius of curvature of the mold part to +/−20 micronswithin a period of one day to six months from the time of producing themold part; b) permanently affixing a uniform and continuous protectivecoating of an inorganic material to at least one of the cavity surfacesof the mold parts to protect the surfaces from chemical attack by themonomers used to make the lens being molded; and c) cast molding atleast one contact lens using the mold assembly, wherein its protectivecoating does not react or coat the lens surface.
 38. The method of claim37, wherein the mold assembly is used once to make an ophthalmic articleand then discarded.
 39. The method of claim 37, wherein cast molding inpart (c) comprises either light or thermal curing or both.
 40. Themethod of claim 37, wherein a glow discharge process is used to applythe inorganic coating to the mold.